"Invariably what you find in family killings, is they are very strongly related with depression."

He said the crimes were often related to family break-ups.

"It's just like a 'you're my property and how dare you leave me' kind of attitude," he said.

"Probably compounded by some depression, unable to cope, can't see a future, a sense of hopelessness and then they act out their frustration and anger.

"The interesting thing is that it's very, very rare to find women killing their own children to get back at their partners.

"Men will kill their own children just to teach their partner a lesson. When you look at crime, it's a purely male phenomenon and 95 per cent of violent crime is committed by males and so it really is males who are going around doing these horrible things."

Professor Guy said that when women killed their children it was usually only associated with depression.

"Not to say that women don't kill, they do, and there are cases of women who've killed their own children, but that's generally in a state of depression," he said.

"[It's] not related necessarily to a family break up, but there are frequent cases, way too frequent cases, of males killing their partners and their children.

"In part it is like, 'if I can't have my children, no one will', and also, 'how dare you leave me, I will teach you a lesson', and it's the ultimate lesson and they know that they are going to cause grief and harm.

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"It's very hard to fathom."

In Margaret River in May, Peter Miles, 61, his 58-year-old wife Cynda, their daughter Katrina, 35, and her four children – daughter Taye, 13, and sons Rylan, 12, Arye, 10, and Kadyn, eight – were found dead at their farm in Osmington on May 11.